National Institute Of Materials Physics - Romania

Publications

5975 articles found

4901. Investigation of trapping levels in standard, nitrogenated and oxygenated Si p-n junctions by thermally stimulated currents

Authors: Pintilie, I; Petre, D; Pintilie, L; Tivarus, C; Petris, M; Botila, T

Published: JAN 11 2000, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 439, 309, DOI: 10.1016/S0168-9002(99)00845-1

The trapping levels induced in p-n Si junctions by irradiation with 24 GeV proton were investigated using Thermally Stimulated Currents (TSC) methods in the 90-300 K temperature range. Several trapping levels, with activation energies between 0.27 and 0.57 eV, were put into evidence. The spatial distribution of the traps was investigated using different wavelengths for the light used to fill the traps. The results lead to the conclusion that the deepest trapping levels are not uniformly distributed in the volume of the sample. For the most important trapping level the average introduction rate was estimated to 0.9-1.2 cm(-1). The activation energy and the capture cross-section of this trapping level seems to depend on the impurity element introduced in Si. (C) 2000 Elsevier Science B.V. All rights reserved.

4902. Experimental evidence of deep electron and hole trapping levels in high fluence proton irradiated p-n Si junctions using optical charging spectroscopy

Authors: Pintilie, I; Tivarus, C; Botila, T; Petre, D; Pintilie, L

Published: JAN 11 2000, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 439, 227, DOI: 10.1016/S0168-9002(99)00887-6

Optical charging spectroscopy (OCS) is first time reported as applied to p-n junctions. The existence of one deep trapping level for electrons and two deep trapping levels for holes was put into evidence, using this method, in proton irradiated p(+)-n-n(+) silicon structures. An analytical formula for the OCS discharging current for this type of structures was deduced. (C) 2000 Elsevier Science B.V. All rights reserved.

4903. The Mossbauer and magnetic resonances investigations of structural phase transitions in K2ZnCl4 crystals

Authors: Constantinescu, S; Grecu, MN

Published: JAN 2000, EUROPEAN PHYSICAL JOURNAL B, 13, 233, DOI: 10.1007/s100510050027

The experimental data carried out by Mossbauer and magnetic resonances investigations of the structural phase transitions in K2ZnCl4 crystals are discussed by a simple electrostatic model, calculating, the lattice contributions to the local electric potential V(r), electric field intensity E(r) a,nd electric field gradient tensor, V-alpha beta(r) and taking into account both the fractional electric point charges and rigid lattice approximations. The validity of the model is proved by a good fit of the computing results and experimental data of quadrupole splitting parameters at K Bites obtained by K-39-NMR methods in high temperature incommensurate phase (similar to Pnam symmetry). The experimental results obtained by Mossbauer and EPR methods in commensurate phase (Pna2(1) symmetry) of iron and copper doped K2ZnCl4 crystals are explained by relaxing the rigid lattice approximation. The insertion of probe ions appear to be done on not-exactly-Zn2+ site.

4904. Crystal-chemistry aspects and electric-field-gradient (EFG) dispersion in Ca-gallogermanate-type structures studied by Mossbauer spectroscopy

Authors: Constantinescu, S; Tarina, D

Published: JAN 2000, EUROPEAN PHYSICAL JOURNAL B, 13, 81, DOI: 10.1007/s100510050011

The crystal field disorder in some trigonal germanates of the type X(3-y)Ln(y)Fe(2+y)Ge(4-y)O(14) (X = Ba, Sr; Ln = La, Nd; y = 0, 1) is studied by Fe-57 Mossbauer effect. The dispersion of the electric field gradient (EFG) at the octahedral sites of these compounds is investigated. A correlation of the experimental and calculated EFG data with some crystal-chemistry aspects is presented.

4905. Experimental investigation of the nonlinear optical response in Fe : PVA

Authors: Bulinski, M; Iova, I; Belea, A; Kuncser, V; Filoti, G

Published: JAN 2000, JOURNAL OF MATERIALS SCIENCE LETTERS, 19, 28, DOI: 10.1023/A:1006739412409

4906. Application of experimental performance criteria for optimal design of angular dispersive powder diffractometers

Authors: Grabcev, B; Tirziu, A

Published: 2000, EUROPEAN POWDER DIFFRACTION, PTS 1 AND 2, 321-3, 161, DOI: 10.4028/www.scientific.net/MSF.321-324.156

The resolution-intensity antinomy is herewith represented by the Experimental performance criterion - luminosity factor couple. The experimental performance criterion, in close relationship but not identical with the resolution, is an entity connected with the object of the experiment. It is proposed as an attempt to introduce a kind of worth-scale for the results of experiments performed with a certain instrument. This concept is used in computer simulation of experiments performed at both thermal neutron - and synchrotron radiation - sources, for determination of the most convenient instrumental parameters of powder diffractometers.

4907. Magneto-thermoelectric alloys obtained by electrodeposition

Authors: Nedelcu, M; Sima, M; Aldica, G; Apostol, E

Published: 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 720, DOI:

When a magnetic field is applied on a narrow gap semiconductor with high hole mobility, a substantial rise in the figure of merit can be observed due to Ethinghausen effect. The most important proof of this effect was achieved by using Bi-Sb alloys. The present paper is devoted to performance of the electrochemical synthesis of Bi-Sb alloys from acid aqueous solutions and to the investigations of physico-chemical. properties of these alloys. Thick films of Bi-Sb alloy were electrodeposited from both chloride and perchlorate solutions. The electro-deposited films obtained from perclorate solutions are thicker, more compact and more uniform. The Bi/Sb ratio in the solution bulk was found to be approximately the same to the Bi/Sb ratio in the electrodeposited alloy. The Hall effect was measured by a home-made apparatus. The range of the magnetic field (B) determined by a standard induction coil was 0.05-1 T. Carrier concentration, n is 10(18) cm(-3) and increases slow in the choosen magnetic range.

4908. Grain-size refinement in Al-Mn-Ce rapidly-quenched alloys

Authors: Nicula, R; Jianu, A; Holzhuter, G; Barfels, T; Burkel, E

Published: 2000, METASTABLE, MECHANICALLY ALLOYED AND NANOCRYSTALLINE MATERIALS, PTS 1 AND 2, 343-3, 32, DOI: 10.4028/www.scientific.net/MSF.343-346.27

Alloys with nominal composition Al94-xMn6Cex (x = 1-4 at.%) and Al99-yMnyCe1 (y = 6, 8 and 10 at.%) were prepared by melt-spinning in protective Ar atmosphere and examined using transmission and scanning electron microscopy (TEM/SEM), selected-area electron diffraction (SAED) and high energy-resolution synchrotron radiation powder diffraction. Depending on the alloy composition, the average size of the icosahedral phase grains could be varied between 2-5 nm up to several hundred nm. The observed grain-size refinement effects open a way for the microstructure control of these novel quasicrystal-based nanocomposite materials and for the fine-tuning of their macroscopic behaviour.

4909. The influence of the material constants and mass-loading on coupling coefficient of monolithic filters

Authors: Mateescu, I; Pop, G

Published: 2000, PIEZOELECTRIC MATERIALS: ADVANCES IN SCIENCE, TECHNOLOGY AND APPLICATIONS, 76, 247, DOI:

Based on Tiersten's analysis an accurate calculation of the coupling coefficient dependence on geometrical dimensions and mass loading for quartz and langasite monolithic structures was performed(1). In this paper we have studied the influence of the material constants on the attenuation characteristics of two-pole langasite monolithic filters by calculation of the dependence between the coupling coefficient and elastic constant c(66), piezoelectric constant e(26) and Voigt's elastic constant gamma (11). We investigated also the effect of mass loading on the coupling coefficient of langasite and quartz monolithic filters and we have found that the effect on langasite filters is lower than on quartz filters. The relation between the coupling coefficient and the material constants is discussed on crystals grown by various laboratories.

4910. Strength of memory-induced anchoring of 5CB on bare untreated ITO

Authors: Dreyfus-Lambez, H; Stoenescu, D; Dozov, I; Martinot-Lagarde, P

Published: 2000, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 352, 460, DOI:

We realize uniform planar alignment of 5CB on isotropic untreated ITO substrate. The counterplate orientation is "imprinted'' on ITO and memorized by adsorption of an oriented nematic layer. We measure the azimuthal and the zenithal anchoring energies. We show that the memory induced anchoring strength is similar to the one usually found for substrates with high anisotropy. Studying rubbed ITO substrate, we show that in this case also the azimuthal anchoring is mainly due to memory effect.